The most important yet least understood aspect of human deglution is the pharyngeal phase of swallowing. A bolus is propelled by contraction of the pharyngeal constrictors to pass through a functional entity known as the upper esophageal sphincter (UES), which relaxes to allow the bolus to pass. However, basic information about the anatomy of the pharyngeal muscles and UES is unknown. These unanswered questions include: the exact nerve supply to the pharyngeal muscles and UES; the neuromuscular compartments of each muscle, and the histological specializations of these compartments. As a result, there continue to be many controversies regarding the pathophysiology of pharyngeal swallowing. In the proposed study, the gross, histochemical and neural compartments of the human pharynx and UES will be studied by a variety of methods which have never been applied to this region. The principle technique will be Sihler's stain (a process developed in the principal investigator's laboratory) which can render large tissue specimens translucent while counterstaining the nerves within them. The unique advantage of the Sihler's stain is that it can be applied to human post mortem material. Other techniques include acetylcholinesterase staining of whole muscles to study the distribution of motor endplate bands, and myofibrillar ATPase staining of muscle sections to determine their activity patterns. The muscles to be studied include the middle and inferior pharyngeal constrictor muscles, cricopharyngeus muscle, and the muscles of the upper esophagus. Preliminary work has been successfully performed with these techniques and, has resulted in some new and important findings. The clinical importance of this project is to provide an anatomic basis for understanding normal and dysfunctional swallowing. One long term goal of this research is the development of a pharyngeal pacer, an implantable neuroprosthesis which could stimulate the pharyngeal muscles to rehabilitate swallowing function in the neurologically impaired. A necessary prerequisite to the development of such a device is a detailed understanding of the neuroanatomy of the region.